In an Ethernet local area network (LAN), broadcasting or broadcast (not to be confused with broadcast as used in the RF art) refers to the transmission of information to be received and processed by all remote devices within the network, despite differing destination addresses. Within the same field, multicast refers to the transmission of information to be received and processed by a limited group of remote devices within the network. Transmissions which are neither broadcast or multicast in nature (non-broadcast) are typically designated for a specific remote device within the network and will not be processed by any other remote devices within the network. For ease of understanding both broadcast and multicast packets may hereinafter be referred to as broadcast packets.
One simple broadcast algorithm is known as flooding. According to this technique, each incoming packet to be broadcast is sent out on every outbound line except the one on which it arrived. Obviously this technique generates a large number of duplicate packets. Typically some method is used to damp or reduce the number of duplicates.
In an Ethernet LAN, a predetermined destination address in the header of a packet identifies the packet as one to be broadcast. Receiving units interpret the packet as being addressed to them if a flood or multicast address is detected in which they are a member. Units which are not part of the selected group will reject the packet as not addressed to them.
Use of flood broadcasting techniques in an RF LAN environment present a unique set of challenges. For instance, the error characteristics of the RF system, especially where the communications path is not line of sight, is typically poorer than the error characteristics of a wired or cable LAN system. A further difficulty is presented if the RF system uses directional or sectorized antennae where only one antenna is active at a time. In this situation, the best antenna utilized by a one remote RF unit when communicating with an RF LAN will probably be different when the RF LAN communicates with yet a different remote device. Multiple antennae choices only tends to complicate the use of flood broadcast techniques in an RF LAN because a signal sent out over a selected antenna simply may not be received by all remote devices within the network.
It would be extremely advantageous therefore to provide a broadcast packet transmission system and protocol capable of resolving these shortcomings.